Many reservoirs containing vast quantities of oil have been discovered in subterranean formations; however, the recovery of oil from some subterranean formations has been very difficult due to the relatively high viscosity of the oil and/or the presence of viscous tar sands in the formations. In particular, when a production well is drilled into a subterranean formation to recover oil residing therein, often little or no oil flows into the production well even if a natural or artificially induced pressure differential exits between the formation and the well. To overcome this problem, various thermal recovery techniques have been used to decrease the viscosity of the oil and/or the tar sands, thereby making the recovery of the oil easier.
One such thermal recovery technique utilizes steam to thermally stimulate viscous oil production by injecting steam into a wellbore to heat an adjacent subterranean formation. Typically, the highest demand placed on the boiler that produces the steam is at start-up when the wellhead, the casing, the tubing used to convey the steam into the wellbore, and the earth surrounding the wellbore have to be heated to the boiling point of water. Until the temperature of these elements reach the boiling point of water, at least a portion of the steam produced by the boiler condenses, reducing the quality of the steam being injected into the wellbore. The condensate present in the steam being injected into the wellbore acts as an insulator and slows down the heat transfer from the steam to the wellbore, the subterranean formation, and ultimately, the oil. As such, the oil might not be heated adequately to stimulate production of the oil. In addition, the condensate might cause water logging to occur.
Further, the steam is typically injected such that it is not evenly distributed throughout the well bore, resulting in a temperature gradient along the well bore. Areas that are hotter and colder than others, i.e., hot spots and cold spots, thus undesirably form in the subterranean formation. The cold spots lead to the formation of pockets of oil that remain immobile. Further, the hot spots allow the steam to break through the formation and pass directly to the production well, creating a path of least resistance for the flow of steam to the production well. Consequently, the steam bypasses a large portion of the oil residing in the formation, and thus fails to heat and mobilize the oil.
A need therefore exists to reduce the amount of condensate in the steam being injected into a subterranean formation and thereby improve the production of oil from the subterranean formation. It is also desirable to reduce the amount of hot spots and cold spots in the subterranean formation.